The greatest concentration of atmospheric contaminants from the exhaust of an internal combustion engine occurs immediately following start-up of the engine. While catalytic converters are required in the exhaust system, such converters are essentially ineffective in controlling pollutants until they are heated to elevated temperatures by the hot exhaust gases, from the engine.
Efforts have been made to control this problem using so called warm-up or "pup converters" which are positioned near the exhaust manifold in advance of a main, under the floor, converter. In some embodiments these converters are heated electrically. Generally the exhaust gases are forced through honeycombed structures the surface of which is coated with a catalyst. While these converters do reduce pollutant emissions following start-up, they are power and fuel consumers. The flow of exhaust gases is impeded throughout the time the engine is operating. In addition to this inefficiency, catalyst in the converter continues to be deactivated as long as the engine is running.